# Free-Space Path Loss Calculator

> Calculate free-space path loss in dB from distance and frequency, and the received signal in dBm from transmit power and antenna gains, for Wi-Fi and radio links.

Category: IT, networking & security · Applies to: Worldwide · Last updated: 2026-10-29
Interactive calculator: https://calculators.geekmidst.com/calculators/free-space-path-loss-calculator

Even with no obstacles, a radio signal spreads out: free-space path loss = 20 log₁₀(4π d f ÷ c). Doubling the distance or the frequency adds about 6 dB.

Also called: FSPL calculator, Wi-Fi path loss calculator, Link budget calculator.

## Inputs
- Distance (default 100)
- Distance unit (options: m, km, ft, miles; default m)
- Frequency (default 2.4)
- Frequency unit (options: MHz, GHz; default GHz)
- Transmit power (unit dBm; default 20)
- Transmit antenna gain (unit dBi; default 2)
- Receive antenna gain (unit dBi; default 2)

## Results
- Free-space path loss
- Received signal
- Received power
- Wavelength

## Formula

```
FSPL (dB) = 20 log₁₀(d) + 20 log₁₀(f) + 20 log₁₀(4π ÷ c) = 20 log₁₀(d km) + 20 log₁₀(f MHz) + 32.45;  Received = Tx power + Tx gain + Rx gain − FSPL
```

Where:
- d: distance in metres
- f: frequency in hertz
- c: 299,792,458 m/s

## Worked example
1. 20 log₁₀(0.1 km) = −20; 20 log₁₀(2,400 MHz) = 67.60.
2. FSPL = −20 + 67.60 + 32.45 = 80.05 dB.
3. Received = 20 + 2 + 2 − 80.05 = −56.05 dBm.

**Result:** Over 100 m at 2.4 GHz, free-space loss is 80.05 dB, so a 20 dBm transmitter with 2 dBi antennas delivers about −56 dBm.

## What the result means

Compare the received level with the receiver’s sensitivity for the data rate you want, and keep a fade margin of 10–20 dB for walls, bodies and multipath, which free space ignores.

## Assumptions and limits
- Clear line of sight with the first Fresnel zone unobstructed, in the far field of both antennas.
- Walls, floors, foliage, rain and reflections are not included; indoor losses are usually much higher than free space.

## Questions

### Why does 5 GHz reach less far than 2.4 GHz?

Path loss rises 20 log₁₀(5 ÷ 2.4) ≈ 6.4 dB at the same distance with similar antennas, and walls absorb more at higher frequencies.

### What is dBm?

Power relative to 1 milliwatt on a log scale: 0 dBm = 1 mW, 20 dBm = 100 mW, −60 dBm = one nanowatt (10⁻⁶ mW).

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Source: GM¹X CalcVerse — https://calculators.geekmidst.com/calculators/free-space-path-loss-calculator